Recent rapid developments in hematology and scientific technology have allowed wide spread of a treatment style that enhances therapeutic effects and reduces side effects in which only a blood fraction necessary for the treatment is separated from a biological fluid such as whole blood, bone marrow, umbilical cord blood, or a tissue extract and administered to a patient without administering unnecessary fractions.
One example thereof is blood transfusion. Red blood cell products are blood products used to treat lack of oxygen caused by hemorrhage, lack of red blood cells, or hypofunction of red blood cells. Because white blood cells may induce an abnormal immunoreaction and a side effect such as graft versus host disease (GVHD), the white blood cells are unnecessary for these products and should be removed using a filter. In some cases, not only white blood cells but also platelets are removed.
Platelet products are blood products used to treat patients with hemorrhage or hemorrhagic tendencies due to lack of a blood coagulation factor. For these products, unnecessary cells and components other than platelets are removed by centrifugation and only desired platelet components are recovered.
Also, hematopoietic stem cell transplants have recently become popular as treatment for leukemia or solid cancers. In the transplants, cells required for the treatment (white blood cells, in particular mononuclear cells) have been separated and administered. In addition to bone marrow and peripheral blood, umbilical cord blood has attracted attention as a source of the hematopoietic stem cells because of its advantages such as small burden on donors and high proliferative ability. Recent studies have suggested that menstrual blood is also rich in stem cells, and this suggestion indicates the possibility of using menstrual blood, which has conventionally been discarded, as a valuable source of stem cells.
In the case of bone marrow or peripheral blood, white blood cells (in particular mononuclear cells) should be separated and purified by removing unnecessary cells and administered. Also in the case of umbilical cord blood, since umbilical cord blood banking for blood relatives has become popular and umbilical cord blood then needs to be cryopreserved until used, white blood cells are separated and purified in order to prevent red blood cell hemolysis that may occur during cryopreservation.
Centrifugation using a specific gravity solution containing ficoll and centrifugation using hydroxyethyl starch as a red blood cell sedimentation agent have been proposed as separation methods, but have a problem of contamination of bacteria and other foreign matter because these processes cannot be carried out in closed systems. Recent documents have also reported cell separation methods in which white blood cells are recovered using a filter material that captures only white blood cells and does not capture red blood cells and platelets, without performing centrifugation (Patent Documents 1 and 2). However, red blood cells and platelets cannot be separated from each other by these methods.
Currently, different separation methods appropriate to respective target components have been used, specifically: separation filters are used for red blood cell products; centrifugation is used for platelet products; and centrifugation using a specific gravity solution or a red blood cell sedimentation agent is used for white blood cell products. Although red blood cells, platelets, and white blood cells can all be theoretically recovered from a single source sample of blood, bone marrow, umbilical cord blood, or the like, the conventional separation methods let useful cells go to waste. This has created a demand for separation techniques that enable red blood cells, white blood cells, and platelets in a single source sample to be separated rapidly without performing complicated operations.
There has been another demand for further improving, in particular, the purity of a mononuclear cell fraction containing hematopoietic stem cells among white blood cells. However, the current techniques still allow high contamination of granular leukocytes, which has created a need to reduce the granular leukocyte contamination to lower levels than the current levels (Non-Patent Document 1).
It has also been suggested that the use of a highly viscous solution containing dextran as a solution for recovering white blood cells or mononuclear cells captured on a filter increases the recovery rates of white blood cells and mononuclear cells (Patent Document 2). This method, however, has a problem that such a dextran solution is so viscous that it is difficult to push it out of a syringe by hand, which in turn has created a demand for separation solutions that enable easy recovering using a syringe and also enable white blood cells or mononuclear cells to be recovered at a high recovery rate.
Patent Document 1: JP 2001-518792 T
Patent Document 2: WO 98/32840
Non-Patent Document 1: TRANSFUSION, Vol. 45, pp. 1899-1908, 2005